Glass-metal seal



Feb. 13, 1940. E. WALDSCHMIDT GLASS-METAL SEAL Filed March 18, 1939 INVENTOR EPA/67" Ii HZDJO /M/DF WWW ATTORNEY Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE GLASS-METAL SEAL Application March 18, 1939, Serial No. 262,708 In Germany March 19, 1938 Claims.

The invention relates to glass-to-metal seals and especially such seals for discharge devices.

An object of the invention is to provide a glass-to-metal seal where the expansion coeffi- 5 cients of both materials are not substantially equal.

Other objects and advantages'of the invention will: be apparent from the following description and drawing in which Fig. 1 is a partial view 0 in cross-section of a discharge device;

Fig. 2 is another partial, cross-sectional view of a modification of the invention disclosed in Fig. 1.

In the preparation of glassto-metal seals, it

has hitherto been considered necessary that the expansion coeiiicients of both materials agree within several per cent of each other. However, conditions often arise in practice wherein this condition cannot be fulfilled. There are several sealing-in materials which are well suited for sealing, but which show other disadvantages.

The sealing-in material which consists of molybdenum, tungsten or an iron-nickel-cobalt alloy which combines very well with glass, has

either a very poor mechanical workability, or a low electrical conductivity, and also a poor thermal conductivity, which qualities often are a great disadvantage in certain devices. Such devices also require the use of quartz, and no metals are known whose expansion coefficients are equal to that of pure quartz.

The invention concerns a sealing-in arrangement which permits the utilization of the desired material of metal and glass, even if the expansion coefficient of the metal varies considerably from that of the vitreous material utilized, such as quartz for example. Specifically stated, the invention provides the sealed-in leads or supports as consisting of thin walled metal tubes which are filled inside at the sealed-in place with a plug of glass or quartz.

It is generally preferred that the plug inside the tube-shaped leads be of the same material, and consequently of the same coefficient of ex- 5 pansion as the vitreous material sealed to the outer wall of the metal lead-in. The metal is of a material and thinness so that it yields readily to the expansion and contraction of the inner and outer vitreous material contacting its walls.

This arrangement permits the utilization of metal and glass having different expansion coefficients.'

A preferred embodiment of the invention is disclosed in Fig. 1. The container l is of glass and has a metal current lead 2 in the form of a thin walled tube, which is sealed at a portion of its outer wall to the tube press 3, vacuum-tight. 0n the inner portion of the hollow tube 2 is a glass plug 4, having direct contact with the inner wall of the hollow tube 2 adjoining the sealing 6 place of the outer wall to the press 3.

It will be noted that this plug extends at least as far as, and in fact farther, on the inside wall than the contact of the press 3 to the outer walls thereof. The tube 2, as illustrated, is very 10 thin and elastic, and the yielding point of the metal is very low. The material of the tube 2 may be one of the metals previously mentioned, namely, molybdenum, tungsten, or an iron-nickel-cobalt alloy, although still other metals, such 16 as nickel, copper, etc., suitable for sealing with glass, may be utilized. The material of the plug 4 is preferably the same as that of the press 3. This material may be hard or soft glass, or quartz.

To obtain better current and heat conduction, the wall of the tube 2 can naturally be strengthened at the places not covered with glass. In case it seems necessary to seal-in larger tubeformed conductors and the fixed wall thickness 25 cannot be lessened, it is possible to compensate for the expansion of the metal tube, that is, for the change in its wall thickness, by choosing the material of the glass plug slightly different from that of the press. The proportions, however, are always such that the total expansion of the lead parts at the sealing-in place is controlled by the expansion properties of the plug I.

An additional use of the invention; is disclosed in Fig. 2 which is particularly adapted II for a quartz seal. The vessel wall, which may be of quartz, is indicated by 5 and is sealed to the outer wall of the metal tube 8 by overlapping its edge I. The quartz plug 9, lying within the tube 8, is preferably integrally connected 40 around the edge I with the container wall, as illustrated at 6. The quartz plug 9 determines the expansion of the metal tube at its place of contact with the container wall. This tube 8 is preferably of molybdenum to withstand the high temperatures used with quartz, and is closed at its inner end ID by means of a glass seal ll of vitreous material well suited for sealing to molybdenum, such as borosilicate glass.

The vitreous material ll may, and preferably 50 does, have a different expansion coefficient from that of the quartz plug 6. A current lead l2 passes through the quartz plug 9 and is sealed, vacuum-tight, through the vitreous seal H, as illustrated. The lead I! does not have to be ias- I tened vacuum-tight in the plug 9 in view of the vacuum-tight seal provided by the vitreous material H at the inner end oi! the tube 8.

In seals of metal bands to glass, there are seal tensions perpendicular to the metal surface continually occurring, since on cooling, the metal contracts more than the surrounding glass and this difference in contraction of both bodies gives rise to leaks in the usual glass-metal combination. The invention provides, however, special pressure forces on the glass body inside the tube so that a stronger contraction of the metal within the elastic limit of the glass plug is prevented and thereby is no formation of strains on the outside glass. As the yield point of the metal utilized is relatively low then, despite great differences in specific expansion, the glass can be as easily sealed to the outer surface of the metal tube as if the metal were not even present, because of the utilization of the glass plug within the metal tube.

The thinness of the tube will, in general, depend on the difference in expansion of the. glass and metal. The greater this difference is, the thinner the tube should be. If a molybdenum tube is used with quartz, then the thickness of the metal should probably be under a thousandth of an inch and be of the order of ten thousandths of an inch. Copper, nickel, etc., used with soft and borosilicate glasses should be of a thinness down at least to the order of thousandths of an inch.

The glass-to-metal seal illustrated in the drawing can be applied to various types of discharge devices, such as those utilized for industrial tubes, radio tubes, lamps, etc. The leads are adapted to be those connected to either the main or auxiliary electrodes. These leads can also be joined in corresponding groups instead of singly. In the example in Fig. 2, it is possible to use several lead wires l2 in place of the Single wire illustrated, especially if a hot cathode is utilized. In fact, many modifications may be made in the form and arrangement of elements, and the specific embodiments illustrated are to be taken in an illustrative sense and not in a limiting sense.

I claim:

1. A seal comprising a vitreous container, a hollow metal tube having its outer wall sealed in said container, said hollow metal tube projecting within said container and having an air-tight closure at its inner end and a plug of vitreous material within said tube at the location where its outer wall is sealed in said container.

2. A seal comprising a vitreous container, a hollow metal tube having its outer wall sealed in said container, said hollow metal tube projecting within said container and having an air-tight closure at its inner end and a plug of vitreous material within said tube at the location where its outer wall is sealed in said container, sealed to said tube, said plug and the portion of said container being of material having substantially the same coefllcient or expansion.

3. A seal for a discharge device comprising a vitreous container, a hollow metal tube having its outer wall sealed in said container, vitreous material within said hollow metal tube in contact with the inner wall adjoining the portion of the outer wall sealed in said container, a conductor extending through said vitreous material and tube, and a second vitreous material sealed to said conductor and inner end of said hollow tube.

4. A seal for a discharge device comprising a vitreous container, a hollow metal tube having its outer wall sealed in said container, vitreous material within said hollow metal tube in contact with the inner wall adjoining the portion of the outer wall sealed in said container, a conductor extending through said vitreous material and tube, and a second vitreous material sealed to said conductor and inner end of said hollow tube, said first vitreous material within said tube having substantially the same coefficient of expansion as the portion of the container sealed to the outside wall of the tube.

5. A seal for a discharge device comprising a vitreous container, a hollow metal tube having its outer wall sealed in said container, vitreous material within said hollow metal tube in contact with the inner wall adjoining the portion of the outer wall sealed in said container, a conductor extending through said vitreous material and tube, and a second vitreous material sealed to said conductor and inner end of said hollow tube, said first and said second vitreous material having different coefficients of expansion.

ERNST WALDSCHMIDT. 

